Rhydon is in the Monster and Ground egg groups. There are a lot of pokemon in the same group, and Ground is the most common group. Some of the easy-to-find pokemon are:
- All the starters and their evolutions are in one of those two groups.
- Most Ground-type pokemon
- Ratatta
- Pikachu
- Ponyta
- The Nido- family (Nidoran etc)
- Mareep etc
- Aron etc
- Shinx etc
And Rhyhorn/Rhydon itself of course! Also don't forget:
1. You need a male and female!
2. If the daycare man says "they prefer to play with other pokemon" then they won't breed. But if he says "they don't like each other" or anything else they WILL BREED, but it will take slightly longer.